1D vertically aligned NiCo2O4 nanoneedles anchored on Ni foam as a novel positive electrode for high energy density asymmetric supercapacitors

Abstract

One of the ongoing challenges is the fabrication of energy storage devices with high power and energy densities. This work addresses it by presenting for the first time a new hydrothermal method for synthesizing nickel cobalt oxide (NiCo₂O₄), and using it as an electro-active material for better power and energy densities in supercapacitors. While the XPS, BET and XRD data further validate its successful growth with large specific surface area of 46.13 m²/g, the FESEM and TEM micrographs show micro-flower like morphologies of the NiCo₂O₄ nanostructures comprising of large numbers of intertwined, vertically aligned 1D nanoneedles. At a current density of 0.3 A. g⁻¹, the NiCo₂O₄-based electrode has a remarkable a specific capacitance of 992.3 F. g⁻¹ along with a capacitive retention of 72 % after 5,000 cycles. An asymmetric supercapacitor (ASC) has also been constructed with the 1D vertically aligned NiCo₂O₄ nanoneedles anchored on Ni foam as the positive electrode, the activated porous carbon made from bio-waste as the negative electrode, PVA-KOH gel served as the electrolyte, while polyethylene terephthalate (PET) acts as the separator. The ASC fabricated with this material has been tested and returned a high energy density of 177.1 Wh. kg⁻¹ and power density of 433.3 W. kg⁻¹ at discharging current density of 0.33 A g⁻¹. Consequently, our work lays the groundwork for the preparation of an electrode material based on binary metal-oxide that has a very large capacity and high energy-power densities for use in future energy storage systems.